1. Field of the Invention
The invention relates in general to a hemadynamometer, and more particularly to a hemadynamometer with piezoelectric device to make obvious the changes of the blood pressure wave that corresponds to systolic and diastolic pressure values in order to detect systolic and diastolic blood pressure values.
2. Description of the Related Art
Hemadynamometer becomes an indispensable part of modern people's life as people pay more attention on their health. Hemadynamometers on the market nowadays can be categorized into half-automatic hemadynamometers, automatic hemadynamometers, and auscultation hemadynamometers. An auscultation hemadynamometer includes an air bag, a manual pump, an air exhaust valve, a mercury column, and a stethoscope. The medical workers usually use auscultation hemadynamometers which are usually more precise. When using auscultation hemadynamometer, the medical worker winds the upper arm of the user with the air bag, and inflates the air bag using the pump. The medical workers can read the pressure value from the mercury column. The bag pressurizes the artery of the upper arm and temporarily screens off the blood current going through the upper arm. Consequently, the doctor opens the air drain valve to gradually deflate the pressure inside the bag. When the pressure is smaller than the systolic pressure, blood spurts into the region of the bag and then form a swirl. Therefore, the Korotkov's-sound is created. At this moment, the doctor can detect this Korotkov's-sound by the stethoscope, and the pressure inside the air bag is defined as a systolic pressure. The pressure in the air bag continues to deflate; the Korotkov's-sound can still be heard. Upon the moment that the Korotkov's-sound disappears, the pressure inside the air bag is defined as a diastolic pressure. The entire operation is done manually; it takes a long time and is inconvenient. It is also more difficult for the public to judge the correct systolic and diastolic pressures.
Furthermore, users can also use an automatic blood pressure monitor (for example, an oscillation blood pressure monitor) to find out the systolic and diastolic pressures. Firstly, the oscillating blood pressure monitor is used to find out the maximum amplitude (Amax). Secondly, finding the value of 0.5*Amax (the value 0.5 is obtained by statistics for example), and treat pressure that corresponds to the value of 0.5 Amax as the systolic pressure. Then, the value of 0.8 Amax (the value 0.8 is also obtained by statistics for example) is found out, and the pressure corresponding to the value of 0.8 Amax is defined as the diastolic pressure. But it is very difficult to distinguish the Amax from other neighboring values. If the Amax is incorrect, both the systolic and the diastolic pressures are incorrect.
Furthermore, the Korotkov's-sound-based hemadynamometer compares the magnitude of the pulse wave to the baseline (for example 0.5V). If the magnitude of the pulse wave is greater than 0.5V, a beep sound is created. The pressure inside the air bag corresponding to the appearance of first beep sound is defined as the systolic pressure. Then, the pressure inside the air bag corresponding to the disappearance of beep sound is defined as the diastolic pressure. However, the strength of heart pump of every individual is different and therefore, the magnitude of the pulse wave of every individual is also different. If the same baseline (for example, 0.5 and/or 0.8) is used for every one, erroneous pressure values are found.